Heat-treating gears and the like



Dec. 12, 1944.

F. S. DENNEEN El AL HEAT TREATING GEAR AND THE LIKE Filed Aug. 6, 1941 2 Sheets-Sheet l -1 ,1944. F. s. DENNEEN M. 2,364,623

HEAT TREATING GEAR AND 'IHE LIKE Filed Aug, 6, 1941 2 Sheets-Sheet 2 \Q, 0 I 5:14 I

Q J .35 I as V vibrations and other causes.

Patented Dec. 12, 1944 HEAT-TREATING GEARS AND THE LIKE Francis S. Denneen, Clevcland,and William C. Dunn, Shaker Heights, Ohio, assignors to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Application August 6, 1941, Serial No. 495,594

4 Claims.

The present invention is a continuation in part of our copending application Serial No. 264,530, filed March 28, 1939, now Patent No. 2,277,082,

and relates to heat treated metallic surfaces.

The instant invention is particularly directed to an apparatus by which heat treated surfaces on gears and the like may be attained.

In theheat treatment of metals generally and in the hardening of ferrous metals in particular, there have been no teachings which would enable those skilled in the art to produce hardened zones of metal of predetermined characteristics as to depth and general contour on articles having abrupt or irregular changes in surface form bythe use of electric heat. Surface hardening processes used heretofore were not adapted to the hardening of such surfaces as the contacting surfaces of ear teeth or Splines, the side walls of sliding keys and keyways, the rifled interiors of gun bores, and many other similar surfaces. In the hardening of such surfaces those above enumerated, it is often important that adjacent surfaces as well as the core or metal under the surface, be kept softer in order that it b sufficiently ductile to resist fractures due to shock, For instance, in a gear tooth, the addendum surfaces should be hard in order to resist the abrasion of sliding and rolling contact of other tooth surfaces, while the metal in the" dedendum and at the root of the tooth which does not contact with any wearing or abrasive element, but which is submitted to heavy bending stresses due to the cantilever construction of gear teeth, should remain strong and comparatively ductile to prevent breakage or the formation of incipient fractures. Experience has taught that the brittleness in steel usually increases with hardness, and the greater the brittleness the more the metal is susceptible to the formation of surface cracks or incipient fractures which eventually extend, far enough into the metal to cause complete failure of the section affected.

Our apparatus is applicable not only to gears, but to numerous other articles as hereinafter explained, such as splined shafts, reamers, drills, gun bores, the wearing surface of pulverizing and crushlngmachlnes, friction feed rolls and the like, and to almost any metal article requiring a hardened zone, particularly where there is an uneven surface.

With the aforementioned conditions in view, this invention then has as its chief object the provision of an apparatus whereby th wearing surfaces of a gear may be hardened without det rimenta'l changes affecting other parts of the gear.

Another object is to provide apparatus whereby the addendum portions of all teeth may be hardened simultaneously and uniformly. A\ further object is to provide whereby a portion of a gear after being hardened may be tempered to any desired degree. Numerous other objects will become apparent from the following description in which details of apparatus capable of producing improved results will be defined and new and advantageous steps in the procedure for obtaining such results will be described or suggested to those skilled in the art of heat treating.

Fig. 1 is a longitudinal section illustrating means for heating and quenching gear teeth.

Fig. 2 is a section taken on line 22 of Fig. 1.

Fig. 3 is an elevation substantially as indicated at 33 of Fig. 1.

Fig. 4 is a section similar to that shown in Fig. 2 but illustrating a modification of the apparatus.

Fig.5 is a vertical view, partly in section showing a further modification of our apparatus.

Fig. 6 is a section at 6 of Fig. 5.

While in the accompanying drawings and descrlption the heating is mainly by high frequency induced currents set up in the zones to be hardened, the heating is also accomplished in part by the direct flow of current into the article through electrical contacts established between the article and parts of the apparatus. 1

Referring now to Figs. 1, 2 and 3, we show one form of apparatus for accomplishing the results of our invention. In this apparatus the gear I! is placed so that the lower ends of its teeth 13 engage the ends of radial supports H of the current conducting base H, which base is carried by a support ii and insulated therefrom as shown at It. The ends of the radial supports I! are upturned and formed to receive in current conducting relation the lower ends of the teeth l3 which may be chamfered or rounded, or have square ends, as shown, the supports being formed to correspond with the teeth.

A cover member i8 is assembled with an outer conductor IS, the cover member having a rim portion 20 turned downwardly to engage the upper ends of the teeth in substantially the'same way as supports l'l engage the-lower ends. The cover I8 is insulated from an extension 2| of the base l4 by a bushing 22 and the outer conductor I9 is air insulated from this cover by the air chamber 23 at all places excepting at the annular'contacting area at 24. When the gear has been placed in position between the base and cover, all contacting surfaces including the surfaces at 24 are brought into conducting relationship by means of a plunger 25 acting downwardly on an insulating spacer 26.

When th members are assembled as shown in Figs. 1, 2 and 3, and held in firm pressure engagement, a source of high frequency current is applied at the terminals 21 and 28. This current, if considered as entering at 21, passes upwardly through the conductor I9 into the cover I8 from which it is evenly distributed and caused to flow downwardly through the addendum portions of the gear teeth l3, which serve as cunent conductors, into the base I. This current passes upwardly from the base through extension 2| into the contactor 29 to which terminal 28 is attached.

The current in the conductor l8 mainly follows the conducting ribs 30 and induces heating current in the addendum parts of the teeth I3. will be evident that in passing through the elements of the circuit, the current in all cases flows in circuits parallel with the teeth and always in reverse direction to the tooth current. The current in the addendum portion of a tooth will produce heating in the addendum portion of that tooth, and the inductive effect of current flowing in the axial ribs of the outer inductor adjacent to the top of that tooth will materially enhance this heating by producing a cumulative effect. The flow of current between the terminals 21 and 28 in passing through the teeth adds to the heating effect due to the direct ohmic resistance of the teeth. From the foregoing it will be evident that with sufficient current available at suitable frequency, very rapid heating of the gear teeth is accomplished. After heating, quenching is effected by the flow of a coolant through passages 3| from a jacket space 32 in the outer inductor.

The conducting ribs 30 assume a variety of forms depending on the form and character of the surface zones to be hardened. Further, the number of ribs can be selected to correspond with the power available so that the surfaces can be hardened in groups, several operations sometimes being required to complete the hardening of all the teeth in any one gear.

When only the outer portions of teeth or other projections are to be hardened, the inductor ribs are sometimes formed and arranged as shown at 23 in Fig. 4. Current then flows longitudinally inthe tops of the teeth in such direction as to be opposite to the current in the rib adjacent to the top of the tooth. The top of the tooth is thus heated very rapidly and the heat generated therein flows by conduction toward the root of the tooth heating as much of the tooth as may be desired, the amount of the tooth being heated being determined mainly by the duration of the heating interval. Quench passages are usually arranged as shown at 3i so as to direct quenching fluid along the sides of the ribs and then onto the top edges of the teeth and along the surfaces of the addendum parts of the teeth, thus cooling the ribs as well as quenching the teeth.

Heating of the teeth may be accomplished by either direct flow of current or by combining this with induced current in the apparatus illustrated in Figs. 5 and 6. As shown in these figures, the gear 33 is supported with the ends of its teeth in conducting contact with an inwardly extending ledge 34 of a cylindrical conductor 35, and is held firmly in position by an upper conductor 36 engaging the opposite ends of the teeth. The parts are held together by a force transmitted from a rod 31 through a lever II having a fulcrum I! carried by a part of the cylindrical conductor 85.

Heating current of suitable character is supplied by conductors 40 and ll. This current in passing downwardly through the cylindrical conductor, which may have such localizing ribs as may be desired, heats this conductor to sufficiently high temperature to cause heat to be transferred to the adjacent teeth of the gear by radiation and conduction. To complete its circuit, this current is required to flow axially through the addendum portion of the gear teeth whereby heat due to ohmic resistance is added to that of radiation and conduction. 'The cumulative heating effect raises the temperature of the tops of the teeth with sufficient rapidity to bring these to hardening temperature before heat has penetrated harmfully into the dedendum or root portion of the teeth. After the teeth are brought to the desired temperature they \are rapidly quenched by projecting against them quench fluid supplied through passages 42 from an insulated jacket 43, the jacket being supplied from a fitting attached at 44. In the apparatus of Figs. 5 and 6 the conductor :5 assumes a variety of forms, depending upon the character of the work required, the contour of the surface zone to be provided thereon, and the current available.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the structure herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

We, therefore, particularly point out and dis tinctly claim as our invention:

1. In apparatus of the character described for simultaneously heating a multiplicity of teeth on a gear, in combination a base comprising a multiplicity of contacting surfaces, the said surfaces being spaced from each other to correspond in position with the teeth of the gear, each surface being adapted to engage an end of a gear tooth corresponding therewith, a cover member havin a multiplicity of contacting surfaces, the said last named surfaces being spaced to correspond with the teeth of the gear, each surface being adapted to engage an end of the gear tooth lying opposite to the end to be engaged by the contacting base surface, a multiplicity of substantially parallel conductor elements, each element having a surface adapted to lie in substantially parallel and closely spaced relation with a corresponding surface of an adjacent gear tooth, each conductor and the gear tooth adjacent thereto being connected in reverse series relation to each other and being connected to a source of inducing current by corresponding contact surfaces of the base and cover to heat the said adjacent gear tooth, the current in each tooth and in its corresponding spacial conductor being substantially in parallel relation with current in an adjacent tooth and adjacent conductor, and pressure means for simultaneously clamping the gear teeth between the base and the cover.

2. In apparatus of the character described for simultaneously heating a multiplicity of teeth on a gear, in combination, a base comprising a multiplicity of contacting surfaces, the said surfaces being spaced from each other to correspond in position with the teeth of the gear, each surface being adapted to engage an endof a gear tooth corresponding therewith, a cover member having a multiplicity of contacting surfaces, the said last named surfaces being spaced to correspond with a tooth of the gear, each surface being adapted to engage an end of the gear tooth lying opposite to the end to be engaged by the contacting base surface, a cylindrical shell extending parallel to and spaced from top parts of the teeth, the said shell carrying a multiplicity of substantially parallel conductor elements, each element having a surface adapted to lie in substantially parallel and closely spaced relation with a corresponding surface of an adjacent gear tooth, each conductor and the gear tooth adjacent thereto being connected in reverse series relation to each other and being connected to a source of inducing current by corresponding contact surfaces of the base and cover to heat the said adjacent gear tooth, the current in each tooth and in its corresponding spacial conductor being substantially in parallel with current in an adjacent tooth and adjacent conductor, and pressure means for clamping the gear teeth between the base and the cover.

3. In apparatus of the character described for heating a plurality of teeth on a gear, in combination, a substantially cylindrical shell comprising an enclosure for the gear, the shell having a radially extending flange at one end serving as a part of the enclosure, contact surfaces associated with the flange to engage end parts of the gear teeth in current conducting relation, a clamping member comprising a radial flange to engage opposite end parts of the gear teeth, the cylin-, drical shell having longitudinal ribs extending radially from a surface "or the shell, each rib being formed to enter a space between two adjacent teeth of the gear in current inducing relation with surface zones of said teeth, means for connecting said shell and said clamping member in a circuit of periodically varying current to cause inducing current to flow in opposite directions in each of said ribs and in the tooth adjacent thereto to heat the surface zone of the tooth. 4. An apparatus of the character described for hardening contact surfaces of adjacent gear teeth having in combination, a base comprising surfaces adapted to engage an end of each tooth, a cover having surfaces adapted to engage ends of the teeth opposite to the ends to be engaged by the base surfaces, a conductor having a part adapted to extend longitudinally in a space between said teeth and to lie in substantially parallel and closely spaced relation with the contact surfaces of both of the teeth and in wide spaced relation with a root surface between the teeth, means for clamping the teeth between the base and the cover to establish current conducting contact between the base and the teeth and between the cover and the teeth, and means for causing periodically varying current to flow in series thru the said part of the conductor, thru the cover, thru the gear teeth and thru the base to heat the teeth. FRANCIS S. DENNEEN.

WILLIAM C. DUNN. 

